Heterojunction bipolar transistors

ABSTRACT

The present disclosure relates to semiconductor structures and, more particularly, to heterojunction bipolar transistors and methods of manufacture. The structure includes: a collector in a semiconductor substrate; a subcollector in the semiconductor substrate; an intrinsic base over the subcollector; an extrinsic base adjacent to the intrinsic base; an emitter over the intrinsic base; and an isolation structure between the extrinsic base and the emitter and which overlaps the subcollector.

BACKGROUND

The present disclosure relates to semiconductor structures and, moreparticularly, to heterojunction bipolar transistors and methods ofmanufacture.

Bipolar transistors can be vertical transistors or lateral transistors.Vertical bipolar transistors can be used for many different types ofapplications, e.g., ranging from high performance applications to lowperformance applications. For example, bipolar transistors can be usedin mm-wave power amplifiers and low noise amplifiers, automotive radarsand optical interconnects.

Typically, heterojunction bipolar transistors are formed in bulksubstrate or in a cavity touching a handle wafer for asemiconductor-on-insulator (SOI) substrate. To manufacture thesedevices, many complex and costly processing steps are required such asepitaxial growth processes and masking processes. These processes can bevery repetitive during the fabrication processes leading to additionalunwanted costs.

SUMMARY

In an aspect of the disclosure, a structure comprises: a collector in asemiconductor substrate; a subcollector in the semiconductor substrate;an intrinsic base over the subcollector; an extrinsic base adjacent tothe intrinsic base; an emitter over the intrinsic base; and an isolationstructure between the extrinsic base and the emitter and which overlapsthe subcollector.

In an aspect of the disclosure, a structure comprises: a collector; asubcollector electrically connected to the collector; an intrinsic baseover the subcollector; an extrinsic base adjacent to the intrinsic base;a hardmask between the collector and the extrinsic base; and an emitterover the intrinsic base.

In an aspect of the disclosure, a method comprises: forming in a singleepitaxial growth processing pass: a collector in a semiconductorsubstrate; a subcollector in the semiconductor substrate; an intrinsicbase over the subcollector; an extrinsic base adjacent to the intrinsicbase; and an emitter over the intrinsic base; and forming an isolationstructure between the extrinsic base and the emitter and which overlapsthe subcollector.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the presentdisclosure.

FIG. 1 shows a heterojunction bipolar transistor in accordance withaspects of the present disclosure.

FIG. 2 shows a heterojunction bipolar transistor in accordance withadditional aspects of the present disclosure.

FIG. 3 shows a heterojunction bipolar transistor in accordance withanother aspect of the present disclosure.

FIG. 4 shows a heterojunction bipolar transistor in accordance with yetadditional aspects of the present disclosure.

FIGS. 5A-5D show fabrication processes of forming the heterojunctionbipolar transistors of FIGS. 1-3 in accordance with aspects of thepresent disclosure.

FIGS. 6A and 6B show fabrication processes of forming the heterojunctionbipolar transistor of FIG. 4 in accordance with aspects of the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure relates to semiconductor structures and, moreparticularly, to heterojunction bipolar transistors and methods ofmanufacture. More specifically, the heterojunction bipolar transistorsmay be self-aligned SiGe vertical heterojunction bipolar transistorswith a subcollector, emitter and base regions manufactured in a singleepitaxial growth process. Advantageously, the present disclosureprovides a lower cost technology by reducing the number of epitaxialgrowth passes, while also reducing mask count.

In more specific embodiments, the heterojunction bipolar transistorsinclude a subcollector, intrinsic base, extrinsic base, emitter andoptional marker layer formed in a single epitaxial processing pass(e.g., step). The emitter and extrinsic base may be separated by atrench filled with dielectric material. In embodiments, the trenchfilled with the dielectric material may be between the emitter and theextrinsic base, in addition to straddling or overlapping thesubcollector (e.g., N− subcollector region) and underlying hardmask. Thetrench filled with the dielectric material and the extrinsic base may belocated over hardmask material. Moreover, in embodiments, the extrinsicbase may be located above a SiGe marker layer. The SiGe marker layer mayhave a lower Ge concentration than the intrinsic base, as an example.The extrinsic base may also be laterally connected to the intrinsic baseon a side.

The heterojunction bipolar transistors of the present disclosure can bemanufactured in a number of ways using a number of different tools. Ingeneral, though, the methodologies and tools are used to form structureswith dimensions in the micrometer and nanometer scale. Themethodologies, i.e., technologies, employed to manufacture theheterojunction bipolar transistors of the present disclosure have beenadopted from integrated circuit (IC) technology. For example, thestructures are built on wafers and are realized in films of materialpatterned by photolithographic processes on the top of a wafer. Inparticular, the fabrication of the heterojunction bipolar transistorsuses three basic building blocks: (i) deposition of thin films ofmaterial on a substrate, (ii) applying a patterned mask on top of thefilms by photolithographic imaging, and (iii) etching the filmsselectively to the mask. In addition, precleaning processes may be usedto clean etched surfaces of any contaminants, as is known in the art.Moreover, when necessary, rapid thermal anneal processes may be used todrive-in dopants or material layers as is known in the art.

FIG. 1 shows a heterojunction bipolar transistor in accordance withaspects of the present disclosure. The heterojunction bipolar transistor10 includes a semiconductor substrate 12 with a subcollector 14. Inembodiments, the semiconductor substrate 12 may be composed of anysuitable semiconductor material including, but not limited to, Si, SiGe,SiGeC, SiC, GaAs, InAs, InP, and other III/V or II/VI compoundsemiconductors. In further embodiments, the semiconductor substrate 12may be a p-substrate with any suitable crystallographic orientation(e.g., a (100), (110), (111), or (001) crystallographic orientation).

The subcollector 14 may be a highly doped N-type subcollector 14 formedby a conventional ion implantation process as is known in the art anddescribed in more detail with respect to FIG. 5A. In embodiments, thesubcollector 14 may be heavily doped with n-type dopants, e.g., Arsenic(As), Phosphorus (P) and Antimony (Sb), among other suitable examples.

Hardmask materials 16, 18, 20 may be formed over the subcollector 14. Inembodiments, the hardmask materials 16, 20 may be nitride and thehardmask material 18 may be an oxide. In alternative embodiments, asingle insulating material or any combination of dielectric materialsdescribed herein are contemplated for use as the hardmask. The hardmaskmaterials 16, 18, 20 may be formed by conventional deposition methods,e.g., chemical vapor deposition (CVD) processes.

Still referring to FIG. 1 , a collector 22 may formed within a trenchextending into the subcollector 14 and hardmask materials 16, 18, 20. Inthis way, the collector 22 may be electrically connected to thesubcollector 14. An intrinsic base 24 may be formed over the collector22. In embodiments, the intrinsic base 24 may laterally extend over,e.g., overlap, the hardmask material 20. Also, an emitter 26 may beformed over the intrinsic base 24 with an optional marker layer 28formed over the emitter 26 and the hardmask material 20. The emitter 26may be N+Si material, as an example. In embodiments, the shape of thesubcollector 14, intrinsic base 24 and the emitter 26 may be different.An extrinsic base 30 is formed on, e.g., directly contacting, the markerlayer 28 and a side of the intrinsic base 24. To reduce processing stepsand costs, the collector 22, intrinsic base 24, emitter 26, optionalmarker layer 28 and extrinsic base 30 may be formed in a singleepitaxial growth pass (e.g., within the same processing chamber) asdescribed in more detail with respect to FIG. 5B.

In specific embodiments, the collector 22 may be an N− subcollectorcomposed of, e.g., lightly doped Si; whereas the intrinsic base 24 andthe marker layer 28 may be SiGe material. The Ge concentration of themarker layer 28 may be less than the Ge concentration of the intrinsicbase 24. For example, the Ge concentration of the marker layer 28 may bebelow 15% and, more preferably about 5%-15%, whereas the Geconcentration of the intrinsic base 24 may be above 15%. The emitter 26may be N+ Si material.

In embodiments, the extrinsic base 30 may be a polysilicon material and,more specifically, a P+ polysilicon material formed by an epitaxialgrowth process following by a patterning process as described in moredetail with respect to FIGS. 5B and 5C. A trench filled with dielectricmaterial 32 separates, i.e., electrically isolates, the extrinsic base30 from the emitter 26. The trench filled with the dielectric material32 straddles or overlaps the collector 22 and the hardmask material 20.Sidewall spacers 33 may be provided on the opposing sidewalls of theextrinsic base 30. In embodiments, the sidewall spacers 33 may be a samematerial as the dielectric material 32.

An interlevel dielectric material 34 may be formed, e.g., deposited,over the trench filled with dielectric material 32, extrinsic base 30,emitter 26 and optional marker layer 28. In embodiments, the interleveldielectric material 34 may be alternating layers of oxide and nitride,as an illustrative example. Contacts 36 may be formed in (e.g., intrenches) the interlevel dielectric material 34 to the extrinsic base30, subcollector 14 and emitter 26. Prior to forming the contacts 36,silicide contacts 35, e.g., NiSi, may be formed on the extrinsic base30, subcollector 14 and emitter 26 as described in more detail in FIG.5D.

FIG. 2 shows a heterojunction bipolar transistor 10 a in accordance withadditional aspects of the present disclosure. In the heterojunctionbipolar transistor 10 a of FIG. 2 , the marker layer is removed from theupper surface of the emitter 26. The remaining features are similar tothat already described with respect to FIG. 1 .

FIG. 3 shows a heterojunction bipolar transistor 10 b in accordance withanother aspect of the present disclosure. In the heterojunction bipolartransistor 10 b of FIG. 3 , the marker layer is removed from the uppersurface of the emitter 26 and between the hardmask material 20 and theextrinsic base 30. The remaining features are similar to that alreadydescribed with respect to FIG. 1 .

FIG. 4 shows a heterojunction bipolar transistor 10 c in accordance withyet additional aspects of the present disclosure. In the heterojunctionbipolar transistor 10 c of FIG. 4 , dielectric material 32, 38 may beformed in the trench between the extrinsic base 30 and the emitter 26.The dielectric material 32, 38 may be oxide and a nitride, with eitherthe oxide or nitride being a sidewall spacer on the emitter 26 and theextrinsic base 30, and the other material filling the remaining portionof the trench. Moreover, the intrinsic base 24 may be doped, e.g., pdoped, under the dielectric material 38. In an optional embodiment, themarker layer 28 can also be removed from the upper surface of theemitter 26. The remaining features are similar to that already describedwith respect to FIG. 1 .

FIGS. 5A-5D show fabrication processes of forming the heterojunctionbipolar transistors of FIGS. 1-3 in accordance with aspects of thepresent disclosure. More specifically, FIG. 5A shows the subcollector 14within the semiconductor substrate 12, and hardmask material over thesubcollector 14. In embodiments, the subcollector 14 may be formed by anion implantation process that introduces a concentration of a dopantinto the semiconductor substrate 12.

By way of example of forming the subcollector 14, a patternedimplantation mask may be used to define selected areas exposed for theimplantations. The implantation mask may include a layer of alight-sensitive material, such as an organic photoresist, applied by aspin coating process, pre-baked, exposed to light projected through aphotomask, baked after exposure, and developed with a chemicaldeveloper. Each of the implantation masks has a thickness and stoppingpower sufficient to block masked areas against receiving a dose of theimplanted ions. An annealing process may be performed to drive in thedopant into the semiconductor substrate 12. The subcollector 14 may behighly doped with n-type dopants, e.g., Arsenic (As), Phosphorus (P) andSb, among other suitable examples.

Still referring to FIG. 5A, hardmask materials 16, 18, 20 may be formedover the subcollector 14. In embodiments, the hardmask materials 16, 18,20 may be a combination of nitride and oxide, deposited by conventionalCVD processes. In embodiments, a single hardmask material is alsocontemplated by the present disclosure.

A trench 21 is formed within the semiconductor substrate 12 and hardmaskmaterials 16, 18, 20. In embodiments, the trench is formed byconventional lithography, and etching methods known to those of skill inthe art. For example, a resist formed over the hardmask material 20 isexposed to energy (light) to form a pattern (opening). An etchingprocess with a selective chemistry, e.g., reactive ion etching (RIE),will be used to transfer the pattern from the patterned photoresistlayer to the semiconductor substrate 12 and the hardmask materials 16,18, 20 to form the trench 21 in these materials through the openings ofthe resist. The resist may be removed by a conventional oxygen ashingprocess or other known stripants.

In FIG. 5B, the collector 22, intrinsic base 24, emitter 26, optionalmarker layer 28 and extrinsic base material 30 a may be formed using asingle epitaxial growth pass, i.e., without any intervening processingsteps. That is, unlike in conventional processes, the epitaxial growthprocess is not performed in multiple passes with intervening fabricationprocessing steps. In embodiments, the epitaxial growth process may beperformed in a single pass in a same chamber, as an example. By using asingle pass with no intervening fabrication processing steps, it is nowpossible to clean the surface of the semiconductor materials a singletime prior to the epitaxial growth process, hence saving considerabletime and costs. The surface cleaning step may be a pre-epitaxial wetcleaning process to limit defect. For example, the pre-epitaxial wetcleaning process may be performed with an HF solution.

Still referring to FIG. 5B, the collector 22 may be formed in the trench31 using a selective epitaxial growth process. In embodiments, theepitaxial growth process may include an in-situ doping to form an N−subcollector. The doping may also be auto-doped as is known in the artusing n-type dopants. In embodiments, the collector 22 may be grown to asurface of the hardmask material 20, e.g., planar with the hardmaskmaterial 20.

The intrinsic base 24 may be formed over the collector 22 by acontrolled epitaxially growth process, which results in a slight overlapor lateral growth onto the hardmask 20. In this way, the collector 22and intrinsic base 24 may have a different shape. In embodiments, theoverlap or lateral overgrowth of the intrinsic base 24 onto the hardmask20 may be provided by adjusting the temperature and/or pressure and/orgas flow of the epitaxial growth process as is known in the art. Forexample, an increase in the temperature and pressure may result in suchoverlap onto the hardmask 20. The intrinsic base 24 may be SiGe materialwith a Ge concentration of greater than 15%.

The emitter 26 may be epitaxially grown over the intrinsic base 24. Inembodiments, the epitaxial growth process may be a non-selectiveepitaxial growth process. In embodiments, the emitter 26 may be N+semiconductor material, e.g., N+ Si, which may be formed by an in-situdoping process using n-type dopants during the epitaxial growth process.For example, the n-type dopant may be phosphorus or arsenic. Inembodiments, there should preferably be no lateral overgrowth of theemitter material onto the hardmask 20, hence it being constrained to thesurface of the intrinsic base 24. In embodiments, the shape of theemitter 26 may be different than the shape of the intrinsic base 24.

The optional marker layer 28 may be formed by a non-selective epitaxialgrowth process over the emitter 26 and the hardmask 20. In embodiments,the non-selective epitaxial growth process may be provided by, forexample, adjusting gases within the epitaxial chamber. As should beunderstood by those of skill in the art, the optional marker layer 28may form polycrystalline over the hardmask 20 and a single crystallineover the emitter 26. In embodiments, the optional marker layer 28 may beSiGe with a Ge concentration of less than 15% and, more preferably,about 5% to 15%.

In embodiments, extrinsic base material 30 a may be epitaxially grownover the marker layer 28. In processes in which the optional markerlayer is not used, the extrinsic base material 30 a may be epitaxiallygrown directly on the hardmask 20. In either scenario, the epitaxialgrowth process is a non-selective growth process forming a polysiliconmaterial and, more specifically, a P+ polysilicon material over eitherthe optional marker layer 28 or hardmask 20. The extrinsic base material30 a may be subjected to a planarization process, e.g., chemicalmechanical polishing (CMP).

As shown in FIG. 5C, a capping material 29 may be formed over theextrinsic base material 30 a. The capping material 29 may be a nitridematerial deposited by a conventional CVD process. A patterning processmay be performed to form the extrinsic base 30 and the emitter 26. Inthis patterning process, the extrinsic base 30 will be laterallyadjacent to and in contact with a side of the intrinsic base 24, whileelectrically isolated from the emitter 26.

The patterning process may also form the trenches 31. For example, thepatterning process may form the trenches 31 between the extrinsic base30 a and the emitter 26 to electrically isolate the extrinsic base 30 aand the emitter 26 to ensure that there are no conductive shorts. Thetrenches 31 are patterned to overlap or straddle the collector 22 andthe hardmask 20. The patterning process may be conventional lithographyand etching processes as already described herein such that no furtherexplanation is required for a complete understanding of the presentdisclosure. It should also be recognized by those of skill in the artthat the patterning process, e.g., formation of the trenches 31, mayremove any defective material of the emitter 26, extrinsic base 30 andintrinsic base 24 that resulted from the epitaxial growth process. Infurther embodiments, the marker layer 28 may be used as an etch stoplayer for the formation of the trenches 31.

In FIG. 5D, dielectric material 32, e.g., oxide, may be formed withinthe trenches 31. In embodiments, the dielectric material 32 may beformed by a blanket deposition process, e.g., CVD, followed by ananisotropic etching process. The anisotropic etching process may recessthe dielectric material 32 within the trenches 31, in addition toforming sidewall spacers 33 on opposing sides of the extrinsic base 30.In addition, the anisotropic etching process may remove the cappingmaterial. Alternatively, the capping material may remain over theemitter 26 and extrinsic base 30, depending on the thickness of thecapping material.

Following the etching process, a silicide contact 35 may be formed onthe extrinsic base 30, emitter 26 and subcollector 14. In embodiments,the silicide contact 35 may be formed prior to or after formation of theinterlevel dielectric material 34 as shown in FIG. 1 . By way ofexample, after exposing regions of the emitter 26 and subcollector 14(and the extrinsic base 30 when an interlevel dielectric material isalready deposited) by conventional lithography and etching processes, athin transition metal layer, e.g., nickel, cobalt or titanium, may bedeposited over the semiconductor material. After deposition of thematerial, the structure is heated allowing the transition metal to reactwith exposed semiconductor material forming a low-resistance transitionmetal silicide 35. Following the reaction, any remaining transitionmetal is removed by chemical etching, leaving silicide contact 35 in theactive regions of the device.

As further represented by the structure shown in FIG. 1 , an interleveldielectric material 34 may be formed, e.g., deposited, over thedielectric material 32, the extrinsic base 30, the emitter 26 and theoptional marker layer 28. In embodiments, the interlevel dielectricmaterial 34 may be alternating layers of oxide and nitride, as anillustrative example, deposited by conventional CVD processes. Trenchesare formed within the interlevel dielectric material 34 (and whereapplicable the marker layer 28 and hardmask materials 16, 18 20) toexpose the silicide contacts 35 of the extrinsic base 30, emitter 26 andsubcollector 14. The trenches may be formed by conventional lithographyand etching processes. A conductive material, e.g., tungsten with a TaNor TiN liner, may be deposited within the trenches, followed by aconventional CMP process to remove any excessive material from theinterlevel dielectric material 34.

FIGS. 6A and 6B show fabrication processes of forming the heterojunctionbipolar transistor of FIG. 4 in accordance with aspects of the presentdisclosure. In these fabrication process, after formation of thetrenches 31, a dielectric material 32 may be deposited over thestructure and within the trenches 31 to form sidewall spacers as isknown in the art. A dopant may be introduced into intrinsic base 24through the open space of the trenches 31, e.g., between the sidewallspacers, using an implant process. In this process, the capping layermay be used as a blocking mask during the implant process. The implantmay be p-type implant, e.g., boron, to provide a link up to theextrinsic base 30. In further embodiments, the implant may include Geand/or C to reduce the concentration of boron. In alternativeembodiments, a deposition of borosilicate glass (BSG) layer may bedeposited within the trench 31 followed by an annealing process to linkthe boron to the extrinsic base 30.

In FIG. 6B, a dielectric material 38 can be deposited within theremaining portions of the trench 31. The processes can continue with thesteps shown in FIG. 5D and FIG. 1 .

The heterojunction bipolar transistors can be utilized in system on chip(SoC) technology. The SoC is an integrated circuit (also known as a“chip”) that integrates all components of an electronic system on asingle chip or substrate. As the components are integrated on a singlesubstrate, SoCs consume much less power and take up much less area thanmulti-chip designs with equivalent functionality. Because of this, SoCsare becoming the dominant force in the mobile computing (such as inSmartphones) and edge computing markets. SoC is also used in embeddedsystems and the Internet of Things.

The method(s) as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A structure comprising: a collector in asemiconductor substrate; a subcollector in the semiconductor substrate;an intrinsic base over the subcollector; an extrinsic base adjacent tothe intrinsic base; an emitter over the intrinsic base; an isolationstructure between the extrinsic base and the emitter and which overlapsthe subcollector; and a marker layer underneath the extrinsic base andwhich also covers an upper surface of the emitter.
 2. The structure ofclaim 1, further comprising a hardmask underneath the extrinsic base. 3.The structure of claim 2, wherein the hardmask comprises at least oneinsulator material located between the extrinsic base and the collectorand the intrinsic base laterally extends onto an upper surface of thehardmask.
 4. The structure of claim 2, wherein the isolation structureoverlaps both the hardmask underneath the extrinsic base and thesubcollector.
 5. The structure of claim 2, wherein the collector is in atrench extending into the semiconductor substrate and the hardmask. 6.The structure of claim 1, wherein the extrinsic base contacts a side ofthe intrinsic base over a hardmask material.
 7. The structure of claim1, wherein the intrinsic base comprises a doped material below theisolation structure.
 8. The structure of claim 7, wherein the isolationstructure comprises sidewall spacers and a second material filling aspace between the sidewall spacers, and the doped material is below thesecond material.
 9. A structure comprising: a collector in asemiconductor substrate; a subcollector in the semiconductor substrate;an intrinsic base over the subcollector; an extrinsic base adjacent tothe intrinsic base; an emitter over the intrinsic base; an isolationstructure between the extrinsic base and the emitter and which overlapsthe subcollector; and a marker layer underneath the extrinsic base,wherein the marker layer and the intrinsic base both comprises SiGe, anda Ge concentration of the marker layer is lower than a Ge concentrationof the intrinsic base.
 10. A structure comprising: a collector; asubcollector electrically connected to the collector; an intrinsic baseover the subcollector; an extrinsic base adjacent to the intrinsic base;a hardmask between the collector and the extrinsic base; an emitter overthe intrinsic base, and a marker layer between the hardmask and theextrinsic base.
 11. The structure of claim 10, wherein the marker layercovers an upper surface of the emitter.
 12. The structure of claim 10,further comprising an isolation structure between the extrinsic base andthe emitter and which overlaps both the subcollector and the hardmask.13. The structure of claim 12, wherein the isolation structure comprisessidewall spacers and a second material filling a space between thesidewall spacers.
 14. The structure of claim 10, wherein the collectoris in a trench.
 15. The structure of claim 10, wherein the extrinsicbase contacts a side of the intrinsic base.
 16. The structure of claim10, wherein the intrinsic base laterally extends onto a surface of thehardmask.
 17. A method comprising: forming a collector in asemiconductor substrate; forming a subcollector in the semiconductorsubstrate; forming an intrinsic base over the subcollector; forming anextrinsic base adjacent to the intrinsic base; and forming an emitterover the intrinsic base; and forming an isolation structure between theextrinsic base and the emitter and which overlaps the subcollector,wherein the collector, the intrinsic base, the emitter and the extrinsicbase are formed in a single epitaxial growth process.